Monitoring endangered iguanas on protected island habitats

Adult male (right) Ctenosaura melanosterna with four females basking in the warm afternoon sun on Cayo Menor, the second largest island in the Cayos Cochinos Archipelago

Research into endangered iguana species is underway on islands off the north coast of Honduras. Whilst island populations are better protected than their mainland counterparts, these populations may be threatened by the presence of other iguana species on the islands.

The Black-chested Spiny-tailed Iguana, Ctenosaura melanosterna, occurs on the Cayos Cochino Islands off the north coast of Honduras and in the Rio Aguán Valley on the adjacent Honduran mainland. This species occupies an estimated 1,300 km² and although the total population size is not known, it is estimated to be less than 5,000 mature adults.

Due to severe habitat loss and fragmentation, and to illegal harvesting of eggs and adults, Black-chested Spiny-tailed Iguana population density is declining. The species is listed as endangered, with each population being considered critically endangered by the IUCN (Pasachnik et al, 2011). Cayo Menor (Pequeño), the second largest island in the Cayos Cochinos Archipelago, is home to the largest known single population of Black-chested Spiny-tailed Iguanas.

The island life

The recent increase in the Green Iguana population density on Cayo Menor has raised concerns about inter-specific competition for common resources

Because the Cayos Cochinos Archipelago is within the Cayos Cochinos Marine Protected Area, its C. melanosterna populations are reasonably protected. The island populations are thought to be larger than the mainland ones, but they are nevertheless seriously threatened by poaching for both food and for illegal sale on the international pet trade.

Additionally, although Green Iguanas are not considered an introduced species to these islands (McCranie et al, 2005), because I. iguana and C. melanosterna show a great deal of overlap in both their diets and the habitats they use, the recent increase in the Green Iguana population density on Cayo Menor (J A Frazier pers. obs.) has raised concerns about the potentially negative effects of inter-specific competition for common resources.

Ongoing and future research

Current research is focusing on understanding patterns of the growth and survivorship of Black-chested Spiny-tailed Iguana hatchlings, as well as continued monitoring of the entire island population.

Additionally, we will be investigating the potential impacts of the growing Common Green Iguana population on C. melanosterna on Cayo Menor by estimating feeding efficiency rates and apparent competitive interactions between the species.